Verify that issue you are experiencing is not already reported on the issue tracker

if known - on the corresponding issue page you might find existing workarounds, or a pull-request to try, or submit a new comment or even a pull request to address the problem

Collect information needed to be shared for effective troubleshooting

Fail2Ban version

if your fail2ban is outdated:

try testing a new release -- the issue might have already being fixed in development

if you can't test for some reason -- read the ChangeLog if no similar issues have been fixed in recent releases

Your OS (with its release version) and either you are using stock fail2ban or the one provided by the distribution through a package manager

Your configuration (/etc/fail2ban), in particular any customizations you have done

Relevant parts of /var/log/fail2ban.log file, preferably obtained while running fail2ban with loglevel = 4 (set it in [Definition] section of /etc/fail2ban/fail2ban.conf or /etc/fail2ban/fail2ban.local). Send lengthy (or with long lines) as attachment (see next one)